Device for detecting a pulsating quantity

ABSTRACT

A device for detecting a pulsating variable, for instance the air flowing in the intake tube of an engine, is disclosed in which the signal processing and the correction of the pulsation error are done in an evaluation device which is a constituent of the sensor. At the output of the signal processor, the sensor, for instance a hot-film air flow rate meter, outputs a corrected output signal, which is directly a measure of the variable to be determined, such as the mass of the air flowing in the intake tube of an internal combustion engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device for detecting a pulsating variable andfor generating a variable-dependent signal corrected for pulsation errorand relates in particular to a device for detecting the pulsating mass,or flow rate, of the air aspirated by an internal combustion engine andfor obtaining the mean air mass taken in per segment corrected forpulsation error.

2. Description of the Related Art

For detecting the flow rate of air aspirated by an internal combustionengine, micromechanical air flow rate meters are typically used, whosesensor element is exposed to the flowing air. Since under certainconditions the air mass, or air flow, in the intake tube of the engineis in the form of a pulsating flow in the intake tube, the sensorelement is installed for instance not directly in the intake tube butrather in a flow bypass, in which the pulsations are less pronounced. Insome engines, such as throttle-free engines, however, the intake tubepulsations are especially strong and cannot be compensated for unlessfurther provisions are made.

There are physical limits to the aerodynamic compensation for pulsationerrors. In defining the bypass geometry of the air flow rate meter, thecompensation is furthermore limited by the thermal inertia of thesensor. The pulsation error depends on the parameters of the mean airflow rate and the frequency and amplitude of the pulsations. For rangesof parameters in which the bypass geometry cannot compensate for thethermal error of the sensor, in the final analysis incorrect indicationsremain because of intake tube pulsations. To reduce these incorrectindications, it is proposed for instance in Published, NonexaminedGerman Patent Application DE-OS 44 08 243 that along with a pneumaticpulsation damping, additional electronic filters are used, whichsuitably vary or damp the output signal of the sensor element. Theelectronic filter is a constituent of the sensor and precedes a circuitfor characteristic curve adaptation and characteristic curve limitation;this circuit for characteristic curve adaptation and characteristiccurve limitation is also a constituent of the sensor element. Theelectronic filter must be adapted to the expected signal in such a waythat both high-frequency natural oscillation and the fundamentaloscillation of the pulsation are damped, so that at the output of thefilter, the remaining pulsation amplitude is only slight. From thesignal thus obtained, mean values of the pulsating variable, that is,mean values of the aspirated air mass, are calculated in a followingmicrocomputer, such as the control unit of an internal combustionengine.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved devicefor detecting a pulsating variable and for correcting for pulsation ofthe pulsating variable.

It is a further object of the present invention to provide a device forgenerating a digital signal characteristic of an amount of air takeninto an internal combustion engine from a pulsating airflow during asegment or pulsation period of the engine, which is effectivelycorrected for pulsation error.

It is another object of the present invention to provide a sensor unitfor generating a digital signal characteristic of an amount of air takeninto an internal combustion engine that is corrected for pulsationerror.

According to the invention the device for generating a corrected signaldependent on an amount of air taken into an internal combustion engineduring engine operation, which is corrected for pulsation error due topulsation of the air taken into the internal combustion engine, includes

a sensor element with an analog signal processing means for generatingan uncorrected analog signal in cooperation with the sensor element,which varies according to an air flow rate of said air taken into theinternal combustion engine;

digitizing means for digitizing the uncorrected analog signal to form anuncorrected digital signal;

analyzer means for determining an amplitude of the uncorrected digitalsignal;

means for determining a mean value of the uncorrected digital signal;

memory means with at least one pulsation error characteristic curvestored therein, which represents a functional relationship between thepulsation error and sensor signal parameters, which include average airflow rate, pulsation frequency and pulsation amplitude;

means for determining the pulsation error from the at least onepulsation error characteristic curve and at least one of the sensorsignal parameters; and

means for correcting the mean value of the uncorrected digital signalwith the resulting pulsation error.

In a preferred embodiment of the invention the device is a sensor unitincluding the sensor element so that the mean value is delivered to thecontrol thus relieving the control unit of the necessity of digitizingand correcting the analog signal from the sensor element. Alternatively,the digitizing and analysis of the analog signal from the sensor elementcan take place in the main control unit of the internal combustionengine.

The device according to the invention for detecting a pulsating variablehas the advantage that especially reliable compensation for thepulsation error is obtained, and this can advantageous be adapted todifferent engines and functions reliably under all possible conditions.In an especially advantageous embodiment the pulsation compensation isalready performed in the sensor unit, which relieves a followingevaluation device, such as the microprocessor of an engine control unit.

Advantageously, a pulsation error characteristic curve or graph that istaken into account in the compensation is stored in the sensor unititself. This pulsation error characteristic curve can be ascertained,for instance, at a suitable test bench and can be written into a memoryof the sensor unit before the engine is put into operation. Thepulsation error characteristic curve PK is a function of variousvariables; for instance, PK=f (airflow rate, frequency, amplitude). Theprinciple is equally applicable if a corresponding pulsation errorperformance graph without correction in the HFM is stored in the controlunit.

The further advantages of the invention obtained by the provisionsrecited in the dependent claims. Independently of these advantageousfeatures, there can also be a pulsation error characteristic curve inthe following evaluation device, or in other words in the control unit,and further or additional corrective provisions can be performed in thecontrol unit. The invention is advantageously employed for detecting theair flowing from an engine or internal combustion engine through theintake tube, in which a hot-film air flow rate meter is disposed as asensor in the intake tube.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiments, with reference to the accompanying figures inwhich:

FIG. 1 is a block diagram of a first embodiment of a device according tothe invention for generating a digital signal dependent on an amount ofair taken into an internal combustion engine, which corrects the digitalsignal for air flow pulsation errors; and

FIG. 2 is a block diagram of a second embodiment of a device forgenerating a digital signal dependent on an amount of air taken into aninternal combustion engine, which corrects the digital signal for airflow pulsation errors.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first exemplary embodiment, in which the mass of the airflowing in the intake tube of an internal combustion engine is to bedetected. In general, however, the invention can be applied to allmeasuring devices with which a pulsating variable is measured.

In the exemplary embodiment shown in FIG. 1, reference numeral 10indicates the sensor element. This sensor element is a hot-film air flowrate meter, which is located in the intake tube, not shown, of theengine. The sensor unit shown within the dashed lines includes not onlythe sensor element 10, but also the means for signal processing theelectronic signal US from the sensor element, which is to be describedin further detail below.

The output signal US of the sensor element 10 is delivered first to ananalog signal processor 11. The processed signal from the analog signalprocessor 11 is digitized in the A/D interface 12 and then delivered toan analyzer 15 at branch point 13. In the analyzer 15, the digitalsignal is examined to ascertain its amplitude and the mean value of thedigital signal is determined in means 18. The pulsation amplitude isdetermined in analyzer 15, for instance, from the signal maximum or thesignal minimum. A further possibility for signal analysis would be asliding determination of the so-called rms value (“rms” means root meanssquare; standard deviation) of the sensor signal. The pulsationfrequency of the signal, which can be used to assist the signalanalysis, can be derived from the engine rpm, for instance, or from anitem of segment information stored in the control unit 20. Theassociated evaluation block “segment information frequency” is indicatedby reference numeral 17 in the drawing. This information is alsodelivered to means 16B for determining a pulsation error as well as theinformation obtained from the analyzer 15 regarding the pulsationamplitude and/or also the mean value from the means 19. A pulsationerror characteristic curve is input to the means 16B for determining apulsation error from the memory means 16A. This pulsation errorcharacteristic curve was determined in a manner explained in more detailbelow and also in the summary above and previously stored in the memorymeans 16A.

The term “segment” in an engine means an angular range that extends overtwo revolutions of the crankshaft, divided by the number of cylinders inthe engine. The associated segment information is output from controlunit 20 as a control signal, which is required for various calculationsthat are done in other subsidiary control units. Since the expectedfrequency of the pulsation of the air in the intake tube is dependent onthe engine rpm, or conversely on the length of time that the crankshaftrotates through an angle equivalent to one segment, the pulsationfrequency can be determined from the segment information.

Thus the output signal US of the sensor element 10 is followed by asuitable means 15, 16AS, 16B, 18, 19 for electronic correction, whichreliably cancels out the pulsation error that occurs in conventionalengines. When the pulsation error is known, for instance at full engineload or from test bench measurements, the measurement error can thus becorrected with a pulsation error characteristic curve stored in thesensor unit itself, in which information about the frequency of theintake tube pulsation, its amplitude, and the mean air mass, which isstored in the sensor unit, is evaluated.

Alternatively, in an embodiment with a sensor unit without amicroprocessor as shown in FIG. 2, the special performance graph orpulsation error characteristic curve can be stored in a memory means 16Aof the control unit 20, and the pulsation correction can be done in thecontrol unit 20.

By adding up the sensor signal over one segment, a mean value isobtained in the block captioned “air flow rate segment” 18. This airmass per segment is subjected to an error correction 19, and this errorcorrection is done on the basis of the data taken from the pulsationerror characteristic curve 16. After the error correction, a correctedoutput signal SK is available, which is delivered to the control unit20. The signal processing described is done in the sensor unit itself inthe embodiment of FIG. 1, so that the control unit 20 is alreadyfurnished with a corrected signal SK.

The mean air mass is determined from the sensor signal after onepulsation period or one segment. With this information, the appropriatecorrection is read out from the error performance graph 16, which hasbeen prepared a priori. The air mass, averaged over one pulsationperiod, is then available, fully evaluated, at the output of the sensorunit in the form of a corrected output signal SK. Since this sensorcorrection is already available at the next pulsation period, it isimmediately possible for a new, corrected value to be made availableeven in the event of rapid engine load changes.

What is claimed is:
 1. A sensor unit for generating a corrected signaldependent on an amount of air taken into an internal combustion engineduring engine operation, said corrected signal being corrected forpulsation error due to pulsation of said air flowing into the internalcombustion engine, said sensor unit comprising a sensor element (10)with an analog signal processing means (11) for generating anuncorrected analog signal in cooperation with said sensor element (10),said uncorrected analog signal varying according to an air flow rate ofsaid air taken into said internal combustion engine; digitizing means(12) for digitizing said uncorrected analog signal to form anuncorrected digital signal; analyzer means (15) for determining anamplitude of said uncorrected digital signal; means (18) for determininga mean value of said uncorrected digital signal; memory means (16A) withat least one pulsation error characteristic curve stored therein, saidat least one pulsation error characteristic curve representing afunctional relationship between said pulsation error and at least one ofplural sensor signal parameters, said sensor signal parameters includingaverage air flow rate, pulsation frequency and pulsation amplitude;means (16B) for determining said pulsation error from said at least onepulsation error characteristic curve and said at least one of saidsensor signal parameters; means (19) for correcting said mean value ofsaid uncorrected digital signal with said pulsation error determined bysaid means (16B) for determining; and means for delivering a correctedmean value to a control unit (20) of said internal combustion engine. 2.The sensor unit as defined in claim 1, wherein said sensor element (10)comprises a hot-film airflow rate meter.
 3. The sensor unit as definedin claim 1, wherein information regarding operating conditions of saidinternal combustion engine is input from said control unit (20) to saidmeans (16B) for determining said pulsation error.
 4. The sensor unit asdefined in claim 3, wherein said information regarding said operationconditions includes said engine speed (rpm).
 5. The sensor unit asdefined in claim 1, wherein said means (18) for determining said meanvalue of said uncorrected digital signal averages said uncorrecteddigital signal over a segment of said internal combustion engine duringoperation of said internal combustion engine.
 6. A device for generatinga corrected signal dependent on an amount of air taken into an internalcombustion engine during engine operation, said corrected signal beingcorrected for pulsation error due to pulsation of said air flowing intothe internal combustion engine, said device comprising a sensor element(10) with an analog means (11) for generating an uncorrected analogsignal in cooperation with said sensor element (10), said uncorrectedanalog signal varying according to an air flow rate of said air takeninto said internal combustion engine; digitizing means (12) fordigitizing said uncorrected analog signal to form an uncorrected digitalsignal; analyzer means (15) for determining an amplitude of saiduncorrected digital signal; means (18) for determining a mean value ofsaid uncorrected digital signal; memory means (16A) including said atleast one pulsation error characteristic curve stored therein, said atleast one pulsation error characteristic curve representing a functionalrelationship between said pulsation error and at least one of pluralsensor signal parameters, said sensor signal parameters comprisingaverage air flow rate, pulsation frequency and pulsation amplitude;means (16B) for determining said pulsation error from said at least onepulsation error characteristic curve and said at least one of saidsensor signal parameters; and means (19) for correcting said mean valueof said uncorrected digital signal with said pulsation error determinedby said means (16B) for determining; wherein said analyzer means (15),said means (18) for determining said mean value, said memory means(16A), means (16B) for determining said pulsation error and said means(19) for correcting are accommodated in a control unit of said internalcombustion engine.
 7. The device as defined in claim 6, wherein saidsensor element (10) comprises a hot-film airflow rate meter.
 8. Thesensor unit as defined in claim 6, wherein said means (18) fordetermining said mean value of said uncorrected digital signal averagessaid uncorrected digital signal over a segment of said internalcombustion engine during operation of said internal combustion engine.9. A device for generating a corrected signal dependent on a pulsatingvariable, said corrected signal being corrected for pulsation error, asensor element with an analog signal processing means for generating anuncorrected analog signal varying according to a rate of change of thepulsating variable; digitizing means for digitizing said uncorrectedanalog signal to form an uncorrected digital signal; analyzer means fordetermination of at least one of a mean value and pulsation amplitude ofsaid uncorrected digital signal; memory means with at least onepulsation error characteristic curve stored therein, said at least onepulsation error characteristic curve representing a functionalrelationship between said pulsation error and sensor signal parameters,said sensor signal parameters comprising said mean value, pulsationfrequency and pulsation amplitude; and means for correcting said meanvalue of said uncorrected digital signal with said at least onepulsation error characteristic curve stored in said memory means.